Ultrasonic diagnostic imaging system

ABSTRACT

A digital video recorder is provided which provides digital storage of realtime ultrasonic image sequences, replacing the conventional VCR with a recorder which does not degrade digital ultrasound images by analog conversion and recording. The capacity of the digital video recorder is extended by the ability of the digital video recorder to compress ultrasound image data prior to storage and the ability to decompress compressed image data retrieved from storage for realtime display.

This application claims the benefit of U.S. Provisional application No.60/123,040, filed Mar. 5, 1999.

This invention relates to ultrasonic diagnostic imaging systems and, inparticular, to ultrasonic diagnostic imaging systems which digitallystore and retrieve ultrasonic image information.

One of the advantages that diagnostic ultrasound has had over many otherdiagnostic imaging modalities is the ability to produce realtime images.The advantage has been especially significant in cardiology where thephysiology of a continually moving organ, the heart, are the subject ofstudy. Realtime imaging has been a virtual necessity in echocardiographyas compared with abdominal and obstetrical applications where thetissues and organs being studies are stationary and may be readilyexamined by static imaging. Echocardiologists, like other practitionersof diagnostic ultrasound, make records of their ultrasound examinationsfor subsequent diagnosis, review, and comparison. Since echocardiographystudies use realtime ultrasonic imaging, they are conventionallyrecorded on videotape with a VCR, rather than being recorded staticallyon film or as photographic prints. A VCR has been an essential accessoryfor an echocardiography system for many years.

Over time ultrasonic imaging systems have become increasingly digital,whereas VCRs have remained recorders of analog video signals. Thus ithas been necessary to convert the digital ultrasound images produced bythe digital scan converter of an ultrasound system into modulated andsynchronized video signals before the images can be recorded by a VCR.This conversion does not contribute to the quality of the image, andoften is detrimental to image resolution. This detriment has been viewedas one which must be accepted, however, since the VCR has traditionallyprovided the only efficient means for recording many minutes of live,realtime echocardiographic image sequences.

The present invention is directed to replacing the VCR with anall-digital means for storing realtime ultrasonic image sequences, atrue digital video replacement of the VCR. The present invention allowsmany minutes of realtime ultrasonic image sequences to be stored on anonvolatile, high capacity digital storage medium such as a hard disk,CD-RW, magneto-optical or floppy disk. In a preferred embodiment theuser has the ability to control the degree of compression of the imagedata. A high degree of compression enables an increased number of imagesto be stored on a given digital storage medium. A constructed embodimentof the present invention provides virtual VCR controls whereby the usercan operate the digital video recorder similar to the manner in which heis accustomed to operating a VCR.

In the drawings:

FIG. 1 illustrates in block diagram form an ultrasonic diagnosticimaging system constructed in accordance with the principles of thepresent invention;

FIG. 2 illustrates in greater detail the digital video storage systemand the video processor of the ultrasound system of FIG. 1;

FIG. 3 illustrates in greater detail the codec processor of the digitalvideo storage system of FIG. 2; and

FIG. 4 illustrates a quad screen ultrasound display and the virtualcontrols of an embodiment of the digital video recorder of the presentinvention.

Referring first to FIG. 1, an ultrasonic diagnostic imaging systemconstructed in accordance with the principles of the present inventionis shown in block diagram form. A central controller 120 commands atransmit frequency control 117 to transmit ultrasonic scanning beams ofa desired transmit frequency band. The parameters of the transmitfrequency band, f_(tr), are coupled to the transmit frequency control117, which causes the transducer 112 of ultrasonic probe 110 to transmitthe desired ultrasonic waves. The array transducer 112 of the probe 110transmits ultrasonic energy and receives echoes returned in response tothis transmission. In FIG. 1 these echoes are received by the transducerarray 112, coupled through the T/R switch 114 and digitized by analog todigital converters 115. The sampling frequency f_(s) of the A/Dconverters 115 is controlled by the central controller. The desiredsampling rate dictated by sampling theory is at least twice the highestfrequency f_(c) of the received passband. Sampling rates higher than theminimum requirement are also desirable.

The echo signal samples from the individual transducer elements aredelayed and summed by a digital beamformer 116 to form coherent echosignals. The digital coherent echo signals are then filtered by adigital filter 118. In this embodiment, the transmit frequency f_(t) isnot tied to the receiver, and hence the receiver is free to receive aband of frequencies which is different from the transmitted band. Thedigital filter 118 can thus pass harmonic frequency signals of afundamental transmit band of frequencies. A preferred technique forseparating harmonic signals is described in U.S. Pat. Nos. 5,706,819 and5,951,478. The received echo signals may then be further processed, forinstance by processing to remove artifacts such as speckle, by a digitalsignal processor 124.

The echo signals are detected and processed by either a B mode processor37 or a harmonic signal detector 128 for display as a two dimensionalultrasonic image on the display 50. The echo signals are also coupled toa Doppler processor 130 for conventional Doppler processing to producevelocity and power Doppler signals which may be used to produce acolorflow or power Doppler 2D image. The outputs of these processors arealso coupled to a 3D image rendering processor 162 for the rendering ofthree dimensional images, which are stored in a 3D image memory 164.Three dimensional rendering may be performed as described in U.S. Pat.No. 5,720,291, and in U.S. Pats. Nos. 5,474,073 and 5,485,842, thelatter two patents illustrating three dimensional power Dopplerultrasonic imaging techniques. The signals from the harmonic signaldetector 128, the processors 37 and 130, and the three dimensional imagesignals are coupled to a video processor 140 where they may be selectedfor two or three dimensional display on an image display 50 as dictatedby user selection.

In accordance with the principles of the present invention, the videoprocessor 140 is coupled to a digital video storage (DVS) system 200which processes digital video signals and audio in realtime forrecording, transmission, or reproduction. As FIG. 1 shows, the DVSsystem is coupled to storage, transmission and reproduction media suchas disk drives, printers, networks and modems. The DVS system processesthis information while the user is simultaneously observing the realtimeimage sequence on the display 50. The DVS system also replays recordeddigital video information on the display 50 when commanded to do so. TheDVS system operates as a digital video recorder which replaces theconventional VCR with a realtime, all-digital recorder and playerwithout the analog conversion degradation of the VCR.

Referring to FIG. 2, portions of the video processor 140, the 3D imagememory 164, and the DVS system 200 are shown in greater detail. Digitalimage data produced by any of the aforementioned processors or detectorsis coupled to the input of a digital scan converter 142, which processesand converts received echo information into an ultrasound image of thedesired format, e.g., sector-shaped or rectangular. The image data canalso be stored in a Cineloop® memory 164′. The Cineloop memory is arandom access memory (RAM) temporary storage buffer which can hold anumber of still or realtime images for immediate review or processing.For example, a typical Cineloop memory can hold a loop (realtimesequence which is replayed) of 400 images for continual replay andreview. At a realtime frame rate of 30 frames per second, the Cineloopmemory can hold a twelve second loop, for instance. At lower realtimeframe rates, e.g., 15 frames per second, the loop will play for agreater duration. An image or loop stored in the Cineloop memory isreplayed through the scan converter and a video display processor & D/Aconverter 144, which processes the digital video signals into analogvideo signals with synchronizing pulses for display on a display monitor50. The Cineloop memory can also receive scan converted digital imagesby way of the video display processor & D/A 144, which is useful forassembling and storing a 3D image sequence, as explained in theaforementioned U.S. Pat. No. 5,485,842.

In accordance with the principles of the present invention, digitalvideo signals are coupled to a codec (compression/decompression)processor 202 of the DVS system 200. In a constructed embodiment thedigital video signals are digital RGB (red, green, blue) signals. Thecodec processor assembles received images into formats determined byuser selected protocols, optionally compresses the image data asselected by the user, and puts the processed data onto a host system bus218. The data on the host system bus is directed to the desired storage,transmission or reproduction medium by a CPU 204. The data can be storedon nonvolatile digital storage media, including a hard disk 210, amagneto-optical disk 212, a CD-RW disk 214, or a digital disk 216. Apreferred digital storage device is one using a high density removabledisk media which is capable of holding the data from several ultrasoundstudies such as an LS 120 floppy disk. The ultrasound data can also betransmitted over a fiber optic network by way of a fiber coupler toprinters and other reproduction and storage devices over a 10/100 base-Tnetwork connection, by modem, or by wireless transmitter. In aconstructed embodiment the DVS system is integrated into the ultrasoundsystem and is operated by the ultrasound system's user interface 64(keyboard, control keys, trackball, softkeys, and displayed controls andhand controller).

The DVS system 200 includes a conventional computer sound card 206 todigitize and reproduce audio signals such as audio Doppler ultrasound,and a conventional computer VGA card 208 for the processing ofultrasound image graphics such as patient name and image depth markers.Preferably the CPU 204, sound card 206, and VGA card 208 share the samemotherboard, and a portion of the host system bus 218 is provided by themotherboard. These modules may be connected to the DVS system by variousbus architectures which may be compatible with the specific module. Forexample, the VGA card may be connected to an AGP bus, the sound card andfloppy disk may be connected to an ISA bus, and the hard disk and codecmay be connected to a PCI bus, all of which comprise the host systembus.

Turning to FIG. 3, the codec processor 202 is shown in greater detail.Digital RGB video is received by the processor 202 at the input of anLVDS (low voltage differential signal) receiver 302. At the output ofthe LVDS receiver 302 the digital RGB signals comprise three bytes (red,green and blue) of eight bits each and in a constructed embodiment arereceived at a rate of 24.5 MHz for NTSC signals and 29.5 MHz for PALsignals. The digital video signals are then assembled into a full imageframe in an acquisition frame buffer 306 under control of an acquisitionFPGA (field programmable gate array) controller 304. The acquisitionFPGA controller can also crop an incoming image frame so that only aspecified region of interest of the full image is retained. Theassembled image frame is coupled to a color space converter 310, whichconverts the 24 bit RGB signals into 24 bit YUV signals. The YUV signalsthen may be compressed if directed by the user under control of acompression FPGA controller 314. Compression is performed by a highspeed compression/decompression FPGA 312, which may perform variouslevels of lossy compression such as JPEG, MPEG or wavelet, or losslesscompression such as RLE. The compressed data is stored in a frame buffer316 by the compression controller 314. RLE compression, an interframecompression technique, will operate separately on the Y,U, and Vcomponents of a single image frame. Other compression techniques such asMPEG operate on multiple frames simultaneously. The compressed data istransmitted through a bi-directional FIFO 318 and put on a local bus 320in four-byte words. The compressed frame data is then transferred to CPUmemory by way of a PCI bus 218′ by a DMA controller residing in the PCIbridge 26. At this point the frame data is stored on one of the digitalstorage devices or transmitted or reproduced under control of the CPU204.

When an image sequence is to be stored without compression theacquisition FPGA controller 304 transmits the image frames directly tobiFIFO 330 and onto the local bus 320, from which the image frames arestored under control of the CPU 204. Incoming image sequences may alsobe processed and then stored or displayed without compression. In thisalternative the incoming image frames are transferred from theacquisition FPGA controller 304 to the lookup table 332 and the scalar334 which can, for example, colorize the images and then scale them to adual or quad screen format size. The image frames are then transferredby the display FPGA controller 336 to the local bus 320 by way of thebiFIFO 330, from which the images can be stored, or to the graphicoverlay buffer 340 for transmission by the LVDS transmitter 344 to theultrasound system for display.

The components of the codec processor are all operated under control ofa local processor 322, which transmits control words to the variouscontrollers by way of biFIFOs 318 and 330. The local processor providesrealtime control of the various codec operations as commanded by the CPU204. A memory controller 324 is under control of the local processor anddirects control messages through the biFIFOs to the various controllers.

When video data is to be replayed from one of the storage media anddisplayed, the data retraces its compression path and is decompressed.Under command of the CPU 204 video data retrieved from the storagedevice and transferred over the PCI bus 218′, where it is put on thelocal bus 320 by the DMA controller residing in the PCI bridge 326. Thedigital video data on the local bus 320 is coupled to the compressioncontroller 314 by way of the biFIFO 318, under control of the localprocessor 322. This time the compression controller 314 sends thecompressed data to the compression/decompression FPGA 312 where the datais decompressed and the decompressed YUV data is stored in a framebuffer 316. The controller 314 sends the decompressed data to the colorspace converter 310 where it is reconverted into RGB video. Frames ofRGB video are coupled by way of the acquisition FPGA controller 304 to alookup table 332 which performs operations such as gamma correction andcolor mapping. The output of the lookup table 332 is coupled to a scalar334 which performs magnification or minimization of image frames asrequested by the user. The frame data is then assembled into a desireddisplay frame format such as full, dual or quad screen in a displayframe buffer 338 under control of display FPGA controller 336. Thecontroller 336 synchronizes the previously stored ultrasound image frameto the timing of the ultrasound system's video display processor & D/A144, so that the user can switch seamlessly back and forth betweenstored image sequences and live image sequences currently being producedby the ultrasound system. Graphic data is stored in a graphic overlaybuffer 340 from which it is synchronized to the timing of the storedultrasound image frame so that the ultrasound image can be overlaid withgraphical information as needed. Stored physiological data such as ECGtraces are also synchronized and combined with the ultrasound image inthis manner. The graphical and video physio information is retrievedfrom the storage or transmission medium by the VGA card 208 undercontrol of the CPU 204, is stored in a graphics memory 342, thencombined with the ultrasound image frame in the graphic overlay buffer.The final display frame in 24 bit RGB bytes is applied to an LVDStransmitter 344 and then to the video display processor & D/A 144 fordisplay on the display monitor 50.

When uncompressed images are retrieved from storage for display, theyretrace the path by which they were stored. Uncompressed image data istransferred by the biFIFO 330 to the acquisition FPGA controller 304,from which it can be colorized or mapped by the lookup table 332, scaledby the scalar 334, and put into the desired display format by thedisplay FPGA controller 336. Alternatively the biFIFO 330 can transferthe image data directly to the display FPGA controller 336 for display.

The codec processor 202 also has the ability to combine stored and liveimage sequences in a single realtime display frame. A realtime imagesequence can be stored on one of the digital storage devices, thenretrieved in synchronism with a live realtime image sequence that iscurrently being produced by the ultrasound system. The retrieved imagesequence data is decompressed if necessary, transferred to theacquisition FPGA controller 304, then scaled and formatted by thedisplay FPGA controller for display in one area of a multi-image (dualor quad screen) display. The live image sequence is synchronouslytransferred by the LVDS receiver 302 to the acquisition FPGA controller304, then scaled and formatted by the display FPGA controller fordisplay in another area of the multi-image display. The multi-imageframe is overlaid with graphic data as needed, then transferred fordisplay on the system display 50 by the LVDS transmitter 344.

The ability of the digital video system 200 to record extended durationsof digital ultrasound images approaching that of a VCR is a function ofthe digital information of an image, the capacity of the digital storagemedia, and the speed (bandwidth) and performance of the digitalprocessors used, in particular the CPU 204 which mediates the PCI bus. Afourth factor which has a very significant impact on storage capacitiesis the level of compression selected by the user. In a constructedembodiment an NTSC format image is composed of 480 lines of 640 pixelsper line. With each RGB pixel comprising three bytes, a full image isseen to comprise just under one megabyte of data. Using a 200 MHz CPU,the constructed DVS system 200 can store data on a disk drive at ratesof 10-17 megabytes per second, which translates to the storage ofrealtime image sequences having frame rates of 10-15 Hz. This rate foruncompressed images can be increased appreciably through compression.The constructed embodiment performs lossless RLE compression at levelsup to 4-6:1, and lossy compression such as JPEG at levels up to 25-30:1.The user is provided choices of lossless, low, medium, or highcompression. These choices connote a quality factor of the compressedand then uncompressed images, since the compression is a function of theimage data itself and cannot be quantitatively specified with greatprecision. At these compression levels frame rates of 30 Hz are readilyattainable. Storage of five, ten, or twenty minutes of realtime imagesare possible depending upon the level of compression used. An 8 Gigabytehard disk can thus store many minutes of realtime images and serve thepurpose of a VCR for many echocardiography exams.

Echocardiography images are frequently accompanied by scrolling tracesof physiological functions displayed on the ultrasound image displaysuch as a QRS cardiac waveform. To further enable high speed digitalstorage, the present invention digitizes physiological information suchas ECG, pulse and phono signals and transmits the digital data forstorage in one of the last lines of the 480 lines of image data, lineswhich are not used for ultrasonic image display data. Thus, thephysiological information is simultaneously stored with the image datato which it relates with no increase in the size of the block of imagedata. Audio signals such as Doppler sounds which are producedconcurrently during imaging are digitized by the sound card 206 andstored in synchronization with the concurrent image data. During replaythe digital audio data is routed back over the PCI bus 218 to the soundcard, is converted to an analog signal and reproduced through thespeakers of the ultrasound system during display of the accompanyingimage sequence.

FIG. 4 illustrates a quad display as it would appear on a monitor screen52 when replayed by a digital video storage system of the presentinvention. Since the present invention can replace the standard VCR, apreferred embodiment uses virtual recorder controls 400 displayed on themonitor screen, which the user would intuitively operate much in themanner of the controls or remote control buttons of a VCR. The virtualbuttons of the virtual controls are arranged in a softkey toolbar 400and take advantage of the versatility of direct digital recording byproviding functions not available on the standard VCR. When the userclicks on the first button 402, the user can scan through consecutiveframes in an image sequence, one frame at a time. The user can scanthrough all four image sequences in the quad display simultaneously, orcan click on one of the quad images to highlight it and scan throughonly that sequence of images. In a constructed embodiment the user usesthe select key of the ultrasound system's user interface to select aquad display or virtual button, and then uses the trackball of the userinterface to scan through the image sequence.

The virtual button 404, when clicked on by the user, plays the imagesequences in realtime. When the button 404 is clicked during realtimereplay, the realtime display will pause. Repeatedly clicking virtualbutton 406 will increment the play speed of the images and repeatedlyclicking virtual button 408 will decrement the play speed of the images.Virtual buttons 410 and 412 will skip back to a previous mark in asequence and skip forward to a later mark in the sequence. Marks areplaced at points in sequences when long sequences are trimmed to one ormore short sequences such as a single cardiac cycle which is ofparticular interest to a clinician. Such immediate access of points in asequence of images is not possible with a VCR, since the user mustserially advance or rewind the tape to get to other points in a sequenceor earlier or later sequences. These virtual buttons enable the user todirectly access and instantly replay a trimmed sequence from an editingmark.

An embodiment of the DVS system of the present invention, with its ownCPU and digital storage and response to the user interface of theultrasound system, can execute stored protocols on the ultrasoundsystem. For instance, the constructed embodiment stores protocols forstress echo exams which are carried out in the following manner. Usingthe ultrasound system user interface including selections displayed onthe monitor, the user selects the desired protocol. The stages to beperformed are selected and defined, which for stress echo are theinitial rest stage and the post-exercise stage. The views of the heartto be acquired are selected, such as 2D long axis, 2D short axis, apical4 chamber and apical 2 chamber views. The capture format such as quadscreen is selected, and the compression level is chosen. The capturelength is also chosen, which can be denominated in time, e.g., 1 secondto 5 minutes for each view, or it can be denominated in the number ofcardiac cycles or number of images per view. As these choices are madethe ultrasound system displays the disk capacity and the number ofsequences that can be stored on the selected storage medium at thespecified capture length and compression level. Patient images are thenacquired one view at a time both pre- and post-stress.

The acquired sequences are then replayed on the display and arranged inthe chosen quad format by the display controller 336. The user can editthe image sequences to select out images or heart cycles that are ofparticular interest. As described above, the user can select one of thefour images of the quad display and select the “trim” toolbar. The usercan manipulate the trackball to scroll through the full image sequenceand mark the first and last frames of portions of a full sequence thatare of particular interest. The trimmed sequence can then be stored as anew image sequence. The user can then replay the quad screen display inrealtime for only the trimmed sequence intervals, continually replayingthe image sequences as image loops.

The versatility and flexibility of the digital recorder makes possiblediagnostic tools not previously known. For instance, a dual or quadscreen display can be formed from one or more previously stored imagesequences together with a live image sequence which is just beingacquired. Such a capability is useful when performing a stress echoexamination, for instance. An image sequence of the patient's heart canbe acquired and stored by the DVS system when the patient is initiallyat rest. An image loop of one cardiac cycle of the at-rest heart can betrimmed and prepared for replay. When the heart rate is accelerated byexercise or a cardiotonic adrenergic agent such as dobutamine, the liveheartbeat is displayed alongside the at-rest heartbeat. Display of theat-rest cardiac loop is repetitively triggered by the ECG trigger of thelive heartbeat image sequence. Thus, live realtime images of theaccelerating heart are viewed alongside and in physiological synchronismwith the stored at-rest beating heart loop. The clinician can therebyobserve the effect of the adrenergic agent by comparing the liveheartbeat with the heartbeat of the at-rest heart. When the cliniciannotes the onset of the effect of the agent, he can stop administeringthe drug so that the patient will not undergo an undue amount ofpharmacological stress.

Different sequences in a dual or quad screen display can be replayed atdifferent rates at the same time, enabling images of the heart cycle atresting pulse rate to be played in moving synchronism with images of theheart after exercise. The clinician can thus assess the side-by-sideperformance of the resting and stressed heart with the two realtimesequences of different heart rates apparently moving in synchronism.

What is claimed is:
 1. A digital ultrasound video storage system forstoring and retrieving realtime ultrasonic image sequences in real timecomprising: a user control; a high capacity nonvolatile digital storagemedium; an image display device; a source of realtime digital ultrasonicimage frame data; and an ultrasonic digital image frame data processor,coupled to said source and responsive to said user control, fordirecting digital ultrasonic image frame data having a frame rate of 10frames per second or greater to said digital storage medium for digitalstorage in substantially real time, and for retrieving said digitalultrasonic image frame data from said storage medium for display on saidimage display device in substantially real time.
 2. The digitalultrasound video storage system of claim 1, wherein said image framedata processor further comprises a video data compression anddecompression circuit for compressing digital ultrasonic image framedata prior to storage, and for decompressing compressed digitalultrasonic image frame data after retrieval from storage.
 3. The digitalultrasound video storage system of claim 2, wherein said video datacompression and decompression circuit utilizes one of a lossycompression algorithm or a lossless compression algorithm.
 4. Thedigital ultrasound video storage system of claim 3, wherein said videodata compression and decompression circuit utilizes one or more of thefollowing compression protocols: JPEG, MPEG, RLE or wavelet.
 5. Thedigital ultrasound video storage system of claim 1, wherein said sourceof realtime digital ultrasonic image frame data comprises a source ofdigital ultrasonic color image frame data.
 6. The digital ultrasoundvideo storage system of claim 5, wherein said digital ultrasonic colorimage frame data has a red-green-blue data format.
 7. The digitalultrasound video storage system of claim 6, wherein said image framedata processor further comprises a video data compression circuit, andfurther comprising a YUV conversion circuit for converting said RGB datato YUV data prior to compression.
 8. The digital ultrasound videostorage system of claim 7, wherein said image frame data processorfurther comprises an acquisition frame buffer for storing a full frameof digital ultrasonic image frame data prior to YUV conversion.
 9. Thedigital ultrasound video storage system of claim 1, wherein said highcapacity digital storage medium comprises one or more of the following:a hard disk, a magneto-optical disk, a digital compact disk, and a highdensity floppy disk.
 10. The digital ultrasound video storage system ofclaim 1, further comprising a video display processor, coupled betweensaid ultrasonic digital image frame data processor and said imagedisplay device, for converting retrieved digital ultrasonic image framedata into a form suitable for use by said image display device.
 11. Thedigital ultrasound video storage system of claim 10, wherein said videodisplay processor includes a digital to analog converter for convertingdigital ultrasonic image frame data to analog signals for use by saidimage display device.
 12. The digital ultrasound video storage system ofclaim 1, further comprising means for arranging retrieved digitalultrasonic image frame data for display in full, dual or quad screenformat.
 13. The digital ultrasound video storage system of claim 1,further comprising means for digitally storing and retrieving audioultrasound data.
 14. The digital ultrasound video storage system ofclaim 13, wherein said means for digitally storing and retrieving audioultrasound data includes a sound card.
 15. The digital ultrasound videostorage system of claim 1, further comprising means for digitallystoring graphic ultrasound image information, and for retrieving saidstored graphic ultrasound image data for display with stored ultrasonicimage frame data.
 16. The digital ultrasound video storage system ofclaim 15, wherein said means for digitally storing and retrievinggraphic ultrasound image information includes a VGA card.
 17. Thedigital ultrasound video storage system of claim 15, wherein said storedgraphic ultrasound image data includes physiological data.
 18. Thedigital ultrasound video storage system of claim 1, wherein said usercontrol further comprises means for controlling an ultrasonic diagnosticimaging system.
 19. An ultrasound system with realtime digital videostorage capability comprising: an array transducer for acquiringultrasonic signals from a region of the body being imaged; a digitalbeamformer, coupled to said transducer, for producing coherentultrasonic image signals of said region in a sequence of realtime imageframes; a digital signal processor, coupled to said beamformer, forproducing frames of digital ultrasonic image data in real time; an imagedisplay, coupled to said digital signal processor, for displaying framesof said digital ultrasonic image data in real time; a high capacitynonvolatile digital storage medium; and a digital video storage andretrieval system, coupled to said digital storage medium, said digitalsignal processor, and said image display, for storing said digitalultrasonic image data on said digital storage medium in substantiallyreal time and for retrieving digital ultrasonic image data from saiddigital storage medium for display on said image display insubstantially real time.
 20. The ultrasound system of claim 19, whereinsaid high capacity digital storage medium has a capacity which able tostore in excess of 400 ultrasound frames.
 21. The ultrasound system ofclaim 19, wherein said high capacity digital storage medium has acapacity which is able to store a realtime ultrasonic image sequencewhich has a display duration on replay of greater than 30 seconds. 22.The ultrasound system of claim 19, wherein said high capacity digitalstorage medium has a capacity which is able to store a realtimeultrasonic image sequence which has a display duration on replay ofgreater than one minute.
 23. The ultrasound system of claim 19, whereinsaid high capacity digital storage medium has a capacity which is ableto store a realtime ultrasonic image sequence which has a displayduration on replay of greater than five minutes.
 24. The ultrasoundsystem of claim 19, wherein said digital video storage and retrievalsystem includes a compression/decompression processor which compressesultrasound images prior to storage and decompresses stored compressedultrasound images prior to display.
 25. The ultrasound system of claim24, wherein the degree of compression effected by saidcompression/decompression processor is variable and selectable.
 26. Theultrasound system of claim 24, wherein said compression/decompressionprocessor can execute a plurality of selectable compression algorithms.27. A digital ultrasound video storage system for storing realtimeultrasonic cardiac image sequences in real time comprising: a source ofrealtime digital ultrasonic cardiac image frame data; an image displaydevice coupled to the source for displaying the cardiac image frame datain real time; a high capacity nonvolatile digital storage medium; and anultrasonic digital image frame data processor, coupled to receiverealtime digital ultrasonic cardiac image frame data from the source,which directs the digital ultrasonic cardiac image frame data to thedigital storage medium to digitally store the cardiac image datadisplayed on the image display.
 28. The digital ultrasound video storagesystem of claim 27, wherein the realtime digital ultrasonic cardiacimage frame data has a frame rate of at least ten frames per second. 29.A digital ultrasound video storage system for storing realtimeultrasonic cardiac image sequences in real time comprising: a source ofrealtime digital ultrasonic cardiac image frame data; a source ofrealtime physiological cardiac data corresponding to the realtimecardiac image frame data; an image display device coupled to the sourcesfor displaying the cardiac image frame data and correspondingphysiological cardiac data in real time; a high capacity nonvolatiledigital storage medium; and an ultrasonic digital image frame dataprocessor, coupled to receive realtime digital ultrasonic cardiac imageframe data and corresponding physiological cardiac data from thesources, which directs the digital ultrasonic cardiac image frame dataand the corresponding physiological cardiac data to the digital storagemedium to digitally store the cardiac image data and the correspondingphysiological cardiac data in real time.
 30. The digital ultrasoundvideo storage system of claim 29, further comprising a source of audiocardiac data corresponding to the realtime cardiac image frame data;wherein the ultrasonic digital image frame data processor is coupled toreceive the audio cardiac data so as to digitally store the audiocardiac data in correspondence to the cardiac image data.
 31. A methodfor producing a cardiac image display comprising: acquiring a firstrealtime sequence of images of one or more cardiac cycles; digitallystoring the first sequence of cardiac images on a nonvolatile storagedevice; acquiring a second realtime cardiac image sequence andcorresponding physiological cardiac data; and simultaneously displayingthe first sequence of cardiac images and the second realtime cardiacimage sequence in physiological synchronism.
 32. The method of claim 31,wherein the physiological cardiac data comprises an ECG signal, andwherein the first sequence of cardiac images and the second realtimecardiac image sequence are both displayed in synchronism with the ECGsignal.
 33. The method of claim 32, wherein simultaneously displayingcomprises simultaneously displaying the first sequence of cardiacimages, the second realtime cardiac image sequence, and the ECG signal.